1. Calcitic Limestone: This type is primarily composed of calcite (calcium carbonate, CaCO3). It is formed from the accumulation and cementation of the skeletal remains of marine organisms like corals, mollusks, and foraminifera. Calcitic limestone is usually light-colored, ranging from white to gray.

2. Dolomitic Limestone: This type contains a significant amount of dolomite (calcium magnesium carbonate, CaMg(CO3)2). Dolomitic limestone can form directly from the precipitation of dolomite from seawater or through a process called dolomitization, where calcite in calcitic limestone is replaced by dolomite. Dolomitic limestone is often denser and more resistant to weathering than calcitic limestone.